Koro Sensei, the yellow octopus teacher from Assassination Classroom, has inspired millions with his Mach 20 speed, unbreakable smile, and mission to save Class 3-E. From a human monster to the world’s greatest teacher, his story is equal parts hilarious, heartfelt, and heroic.
Koro-sensei (殺せんせー, “Unkillable Teacher”) is the main protagonist of Yūsei Matsui’s Assassination Classroom (manga 2012–2016, anime 2015–2016). Introduced in chapter 1 and episode 1, he’s a yellow octopus-like creature who blew up 70% of the Moon and threatens to destroy Earth in one year — unless Class 3-E assassinates him. In exchange, he teaches them to kill… and to live.
Koro Sensei Wiki
Full Name
Unknown (formerly Reaper / Shinigami, human name unrevealed)
Anti-sensei BBs, laser grid, heart stab, self-destruct in 1 year
Techniques
Tentacle drills, mucus shields, liquefaction, color emotion change
Notable Battles
vs Class 3-E (daily), vs Gakushū Asano (exam war), vs Government
Koro Sensei Story
Once the world’s deadliest assassin known as The Reaper, he was betrayed, captured, and used in anti-matter experiments by Kotaro Yanagisawa. Turned into a yellow monster, he escapes — but bonds with Aguri Yukimura, Class 3-E’s former teacher. Her death fuels his vow: teach her students to kill him… or become strong enough to live.
His final year:
Assassination Training: Turns rejects into elite killers.
Emotional Growth: Helps every student overcome trauma.
March 13: Lets Nagisa stab his heart — dies smiling, saving Earth.
His legacy: Class 3-E graduates as heroes.
Personality Traits
Koro-sensei is perverted, nurturing, and profoundly selfless:
Pervy Sensei – Nosebleeds at magazines, draws “art” on tests.
Ultimate Teacher – Knows every student’s weakness and dream.
Self-Sacrificial – Chooses death to protect Earth and students.
Childlike Joy – Loves gossip, sweets, and praise.
Koro Sensei Quotes
“The difference between the novice and the master is that the master has failed more times than the novice has tried.”
“Please don’t think of me as a monster. I’m just a teacher.”
“You may kill me… but you must become strong enough to do it with your own hands.”
“Nufufufu~ You’ve grown!”
Popular Fan Theories
Debated in :
Did Koro-sensei let Nagisa win? → Yes — guided the knife himself.
Could he have escaped Earth? → Chose not to; loved students too much.
Is Koro-sensei immortal? → No — 1-year anti-matter decay was real.
Was Aguri his wife? → Symbolic; she was his reason to live.
Unknown or Fun Facts about Koro-sensei
Real Name: Never revealed — even to Class 3-E.
Tentacle Count: 15 (one lost in experiment, regenerated).
Salary: ¥0 — government pays in anti-sensei weapons.
Voice Actor: Jun Fukuyama also voiced Lelouch (Code Geass).
FAQs
Q1. Is Koro Sensei really dead?
Yes — self-destructed to prevent Earth’s destruction.
Q2. What was Koro Sensei before?
The Reaper — world’s #1 assassin, human.
Q3. How fast is Koro Sensei?
Mach 20 (~15,000 mph) — fastest in anime.
Q4. What is Koro Sensei height and weakness?
Height: ~300 cm (9’10”) | Weakness: Anti-sensei BBs, heart stab
